I have a question about the "Acceptance is never absolute" principle and your description of it.
All the principles are addressed to the MC. Is that the case here, or is this Principle one that the players are supposed to follow as well?
I mean, as MC, I can ensure that Bella doesn't accept Edward unconditionally, if she's an NPC. If they are both PCs, however, it's really up to the players.
I sincerely hope that the monsterhearted will give each other only lopsided and conditional acceptance. I can't imagine the play procedures (strings, manipulation, promises, teenager protagonists) leading to anything else.
However, principles are directed at the MC. So, have your NPCs only give out lopsided and conditional acceptance. And when a PC makes an accepting motion towards another PC, follow your principles:
Acceptance is Never Absolute,
so start looking for its fault lines. Start looking for its lopsided-ness and its many conditions. Challenge it.
Ask provocative questions, and build on the answers."Bella, why is Edward only making this promise now? Why didn't he make it when you were alone in the fields together?"
"Edward, what kind of pressures are you under, while you make these promises to Bella?"
Remember,
Happiness Always Comes At Someone Else's Expense.
And so, if Edward and Bella are being lovely and happy and honest with each other,
it's gotta hurt someone.
The bad guy vampires? Jacob? Hungry, hungry Jasper?
Look for the damage done.
So, similar question for your ungiven future advances. If I'm a player, can I just up and declare that now another PC accepts mine or is her soulmate?
I think so.
The "absolute acceptance" one might be reserved for NPCs, or work differently for PC/PC...
But the "you're my soulmate" one can definitely be thrown at another PC. And check it, let's look at Twilight again for a second:
Bella wants Edward, hard. She wants his sex and his vampirism.
Edward is a douche who's afraid of commitment.
Jacob's not afraid of commitment. His cards are on the table. He wants Bella.
While Bella is all "bite me, bite me," it's clear that she's not going to accept Edward unconditionally while she's still human, and she's not even going to commit to him unconditionally while she's still human. So, by the end of the third movie, she still hasn't purchased either of these ungiven futures.
At the end of the second movie, however, Edward takes "You're my soulmate" towards Bella, when he says, "We need to get married."
And during the third movie, Jacob steps up and takes "You're my soulmate" towards Bella, too! And he's all like, "I will wait for you no matter what, and I will defend you no matter what, and check out how awesome my abs are."
And if I were bothering to read the books, I'd know what happens next. So far, no one loves anyone unconditionally. Two boys have declared Bella their soulmate. But Bella ain't married yet, and things could still get real. When's that fourth movie coming out? I heard Bella gets knocked up.